An ink-jet printer using an ink-jet mechanism is disclosed. In the case of color printing, an ink-jet printer is provided with record heads for different colors. Recently, there is an ink-jet printer of type of a line head unit structure having a width greater than the length of a conveyed recording medium in a direction orthogonal to the conveyance direction of the recording medium to meet the desire for high-speed printing.
On the other hand, in order to prevent poor ink jetting from the nozzle of the ink-jet printer, the ink-jet printer needs to be maintained periodically. As normal printing cannot be conducted during the maintenance, printing processing is stopped every time a record head is maintained, thus, the frequent maintenance on record heads disables high-speed printing even in the use of line record heads.
Then, a technology is proposed to maintain the record head for a single color, that is, the record head for black color, during color printing and the record heads for multiple colors excluding black color during monochrome printing. In the technology, the color used in color printing that is equivalent to a black dot is achieved by a composite black composed by a plurality of colors different from black.
However, as prints focusing on colors, such as posters, are the main products of the printing using line record heads, there is a problem that the low image quality caused by the use of the composite black makes it impossible to obtain a desired print.